Currently, both diagnostic and therapeutic catheters are manufactured by forming braided tubes of stainless steel fibers or strands, over a mandrel. More specifically, the braided tube may be formed about an inner Teflon.RTM. liner or tube initially carried on a supporting mandrel. An outer plastic layer may then be extruded about the braided material to create the catheter body. Current catheter constructions also utilize a transition tip which is not reinforced with braid in order that the tip be softer and more flexible than the remaining portions of the catheter. In some catheter designs, an even more flexible tip (also referred to as the terminal tip) is bonded to the free end of the tubular transition tip.
Catheters which incorporate multiple axial sections typically employ butt or lap weld joints to secure the axial sections of the catheter together. See, for example, U.S. Pat. Nos. 5,254,107; 4,861,337; 4,793,351; 4,662,404; and 4,391,302. Some catheter constructions utilize a tapered joint where the terminal tip is joined to the catheter body. See, for example, U.S. Pat. Nos. 4,886,506 and 4,385,635.
Catheters incorporating either butt or lap type welded joints are not completely satisfactory however, and it is thus the object of this invention to improve upon prior catheter constructions by incorporating unique weld configurations which have a substantial axial seam component extending along the axis of the catheter. In other words, adjacent catheter sections (and not including the terminal tip) are cut and welded in such a way that they overlap in the longitudinal direction, but without altering the outer diameter of the catheter. This arrangement not only increases surface area at the weld joints and thereby also increases bond integrity, but also creates a more desirable transition between the same materials of different durometer or different materials with or without the same durometer, than other more conventional welds such as lap or butt welds.
The unique weld configurations of this invention also permit alteration of properties or characteristics of the catheter material in the area of the weld, and this feature is particularly advantageous in areas of the catheter that will be curved, in that different stiffness or hardness materials can be used on the inside and outside portions of the curve.
Examples of the unique weld configurations in accordance with this invention include step joints, taper joints, and combinations of the two.
This invention also relates to an improved method for manufacturing braid reinforced catheters with or without the unique axial weld joints as described above. In the exemplary embodiment, the process relates to the manufacture of a catheter having inner and outer layers sandwiched about a braided tube layer. The inner layer is preferably formed from Teflon.RTM. while the outer layer is provided in the form of three axial jacket sections, one of which comprises nylon and the others of which comprise a polyether block amid (PEBA), such as that commercially available under the name Pebax.RTM..
In the process, a thin walled Teflon.RTM. tube is loaded onto a stainless steel mandrel. In a separate operation, a spring temper stainless steel wire is braided onto a disposable (preferably plastic) mandrel at a specified braid density and with a diameter approximating the diameter of the Teflon.RTM. covered mandrel described above. Predetermined lengths of the braided stock are cut and the disposable mandrel is removed and discarded. One end of the braided wire tube is then placed in an annealing fixture so that about a 1/2 inch long section of the braided tube is annealed. The annealed section is then trimmed to leave approximately a 1/16 inch long section of annealed braid.
Starting with the non-annealed end of the braided tube, the latter is loaded onto the Teflon.RTM. covered mandrel, sliding the annealed section over the end of the Teflon.RTM. tube so that approximately 1 inch of the Teflon.RTM. tube is left exposed. It is desirable to anchor the annealed section of the wire braid to the Teflon.RTM. tube, and this is done using a variety of methods including bonding the annealed wire section to the Teflon.RTM. using adhesives. In accordance with the present process, however, the annealed end portion of the wire braid is anchored to the Teflon.RTM. base using a sleeve of PEBA material applied with a shrink film such as FEP-Teflon. The compressive force generated by the shrink film, combined with the heat inherent in the process of shrinking the film, cause the PEBA sleeve to melt into the interstices of the wire braid at the same time that the wires are being forced flat against the inner Teflon.RTM. layer. This results in the annealed wires being held neatly in place so that they will not be disturbed during the remainder of the catheter assembly process. Using PEBA to achieve this end is desirable in that the various catheter components are kept as homogenous as possible.
In the next process step, a 1/2 inch length of soft terminal tip stock material is threaded over the end of the Teflon.RTM./mandrel assembly so that it comes into contact with the end of the annealed portion of the wire braid described above. To keep the terminal tip in place, a tight press fitted piece of Teflon.RTM. tubing may be threaded onto the Teflon.RTM./mandrel assembly and advanced until it is butted up against the tip stock. This so-called "bumper" will keep the tip stock in place during the remainder of the catheter process, and will also keep the terminal tip material from flowing out of the end of the assembly during the thermal processing which follows.
As mentioned above, the outer layer of the catheter consists of three different extruded sections of tubing which have specific wall thicknesses and inside diameters which are no smaller than the outside diameter of the wire braid. The primary jacket is formed from nylon 12 with 30% BASO.sub.4, and it is approximately 80 cm. in length and forms the main shaft with the catheter. The secondary jacket is PEBA with a Shore D durometer of 70, and again with 30% BASO.sub.4. This secondary jacket is approximately 25 cm. in length. A tertiary jacket is formed from a soft PEBA, with a Shore D durometer of 48 also with 30% BASO.sub.4. This tertiary jacket is approximately 7 cm. in length and generally forms the soft primary curved section of the catheter. It should be noted, however, that PEBA could be substituted in part or all for the nylon 12, and the BASO.sub.4 could consist of more or less than 30%, and other radio paque agents such as but not limited to bismuth subcarbonate and the like may be employed. The axial jackets are cut such that they can be joined using the axial seam weld constructions described above.
The tertiary jacket is first loaded onto the end of the braided tube and Teflon.RTM. inner layer assembly, opposite the end with the annealed section of wire braid and moved axially along the mandrel until it contacts the terminal tip stock. The secondary jacket is then loaded onto the assembly with its weld seam oriented as necessary to the corresponding weld seam of the tertiary jacket. The primary jacket is then loaded in the same fashion.
An FEP shrink tube is loaded over the entire catheter assembly, and the assembly is then placed into an oven or other heated chamber where the FEP shrink tube is heated, causing the now molten jackets to compress into the interstices of the wire braid, contacting and adhering to the etched surface of the Teflon.RTM. liner. After the assembly has cooled to room temperature, the FEP shrink tube and then the stainless steel mandrel are removed. Finally, the soft terminal tip stock can be cut to the desired length and any of a variety of known methods can be utilized to "reflow" the cut end of the tip such that the soft PEBA material flows beyond the end of the Teflon.RTM. liner, leaving the liner encapsulated by a small tip of PEBA material.
Other objects and advantages of the subject invention will become apparent from the detailed description which follows.